Hydrogen is a clean fuel and can be used to efficiently produce electricity in a fuel cell system. A hydrogen fuel cell is an electro-chemical device that includes an anode and a cathode with an electrolyte membrane disposed therebetween. The anode receives a reactant, (e.g. hydrogen gas), and the cathode receives an oxidant (e.g. oxygen or air). The hydrogen gas is disassociated in the anode to generate free hydrogen protons and electrons. The hydrogen protons pass through the electrolyte membrane to the cathode. The hydrogen protons react with the oxygen and the electrons in the cathode to generate water. The electrons from the anode cannot pass through the electrolyte membrane, and thus, are directed through other fuel cell system components before being sent to the cathode. Typically, numerous fuel cells are combined in a fuel cell stack to serve as an energy source and generate a desired power for a system such as a vehicle. Not all of the oxygen is consumed by the fuel cell stack, and some of the oxygen is output as a cathode exhaust fluid that may include water as a fuel cell stack by-product.
The oxygen is supplied to the fuel cell system by a compressor. The compressor is typically powered by a motor which uses a portion of the energy generated by the fuel cell system. Accordingly, an efficiency of the fuel cell system is not optimized.
It would be desirable to produce a fuel cell system including a compressor coupled to a freewheeling expander, wherein the expander assists a motor to power the compressor and optimize an efficiency of the fuel cell system.
An advantage of the freewheeling expander is that the expander can assist the compressor over broad flow and pressure ranges without requiring additional components such as actuators (e.g. wastegate valve, variable turbine geometry), for example. The freewheeling expander is a simple, cost effective, self-regulating means to improve an efficiency of the fuel cell system.